Embodiments of the inventive concept relate generally to electronic memory technologies. More particularly, embodiments of the inventive concept relate to semiconductor memory devices and methods of performing read operations in the semiconductor memory devices.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile semiconductor memory devices, which lose stored data when disconnected from power, and nonvolatile semiconductor memory devices, which retain stored data when disconnected from power. Examples of volatile semiconductor memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM). Examples of nonvolatile semiconductor memory devices include masked read-only memory (MROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM).
Flash memory is a type of EEPROM that has achieved increasing popularity in recent years due to attractive features such as relatively high storage capacity, low power consumption, and an ability to withstand physical shock. Flash memory is currently used in a wide variety of technologies, such as computers, cellular phones, personal digital assistants, digital cameras, camcorders, voice recorders, multimedia players, handheld personal computers, gaming consoles, fax machines, scanners, and printers, to name but a few.
In an effort to increase the storage capacity of flash memory and other forms of nonvolatile memory, researchers have developed so-called multi-bit memory devices. A multi-bit memory device is a device capable of storing more than one bit of data per memory cell. For example, a two-bit flash memory device may store two bits per memory cell. Although storing more than one bit of data in each memory cell may provide increased storage capacity, it can also lead to various complications in device operation, such as decreased read margins and increased error rates.